In recent years, thin display devices such as liquid crystal displays (LCDs) have been widely used in various apparatuses such as personal computers, mobile phones, personal digital assistants (PDAs), and game machines. Display devices having a touch panel stacked on a display panel to detect position information on a display screen are also known in the art.
Examples of known types of touch panels include a resistance film type and an optical type.
In the resistance film type, a transparent conductive film is bonded to both the surface of a substrate bonded to a display panel, and the surface on the substrate side of a film bonded to the surface of the substrate with a small gap therebetween. The transparent conductive films contact each other at a position touched by a finger, a pen tip, etc., and a current flows therebetween, whereby the touched position is detected.
However, in the configuration in which the touch panel is stacked on the display panel, light is reflected from the surface of the display panel, the back surface of the touch panel, the inside of the touch panel, and the front surface of the touch panel, whereby display contrast is reduced.
Moire patterns are also produced by the interference between the reflected light beams, thereby reducing the display quality. Moreover, the structure in which the touch panel is stacked on the display panel increases the overall thickness of the display device, and also increases the weight thereof.
Thus, it is proposed to integrate a resistance film type touch panel with a display panel (see, e.g., Patent Documents 1 and 2).
Patent Document 1 discloses that first touch electrodes are stacked over gate lines and source lines of a TFT substrate of a liquid crystal display (LCD) panel, and second touch electrodes are stacked over a black matrix of a counter substrate of the LCD panel, so that the first and second touch electrodes are formed in a grid pattern.
Patent Document 2 discloses that a plurality of protruding portions are formed in a TFT substrate so as to protrude toward a counter substrate, and the surface of each protruding portion is covered by an electrode. Position information is detected by detecting a change in electric capacitance between the electrode on the protruding portion and a counter electrode, or a change in resistance of the electrode and the counter electrode.